This application claims the priority of Japanese Patent Document Nos. 2002-012488 and 2002-075392, filed Jan. 22, 2002, and Mar. 19, 2002, respectively, the disclosures of which are expressly incorporated by reference herein.
1. Field of the Invention
The present invention relates to an exhaust gas purifying device and method for an internal combustion engine.
2. Conventional Art
Generally, when a motor vehicle use exhaust gas purifying catalyst such as a lean NOx catalyst and a three-way catalyst excessively traps therein moisture exhausted from the internal combustion engine thereof, soluble components in the catalyst sometimes elute and the purifying performance thereof sometimes reduces.
For this reason, for example, JP-A-7-158425 (1995) proposes to estimate moisture deposition amount on NOx catalyst from exhaust gas based on the amount of fuel fed to an internal combustion engine and to accumulate the same, and then to estimate deterioration of the NOx catalyst, and JP-A-11-6424 (1999) proposes to estimate moisture amount adsorbed on an HC adsorbent and to effectively perform a post treatment of HC released from the HC adsorbent in accordance with temperature rising speed variation of the HC adsorbent which varies depending on the amount of moisture.
However, the above referred to conventional art does not go beyond the estimation of the amount of trapped moisture in the catalyst and not relate to removal of the trapped moisture.
Accordingly, the conventional exhaust gas purifying devices caused the following problem, in that when the temperature of the catalyst does not rise more than the moisture evaporation temperature such as in a short time operation immediately after starting the internal combustion engine, the moisture generated does not evaporate and remains in the catalyst, thereby, if such short time operation is repeated, the moisture accumulates in the catalyst and soluble components in the catalyst elute which reduces the purifying performance of the catalyst.
In view of the above problems, an object of the present invention is to provide a device and a method which estimate amount of moisture trapped in the catalyst and remove the moisture trapped in the catalyst.
In order to resolve the above object, the present invention is provided with a trapped moisture amount estimation means which estimates amount of moisture exhausted from an internal combustion engine and trapped in a catalyst, a judgement means which judges whether the estimated value of the trapped moisture amount exceeds a predetermined amount, and means for controlling removal of the moisture trapped in the catalyst, wherein when the estimated value of moisture trapped in the catalyst exceeds the predetermined value, removal of the moisture in the catalyst is performed.